


Crashing Together

by SereneCalamity



Category: Shadowhunters (TV), The Mortal Instruments (Movies), The Mortal Instruments Series - Cassandra Clare, The Shadowhunter Chronicles - Cassandra Clare
Genre: Alternate Universe, Anal Sex, Established Relationship, Explicit Sexual Content, F/M, Oral Sex, Polyamory, Resolved Sexual Tension, Roommates, Threesome - F/M/M, kind of?
Language: English
Status: Completed
Published: 2019-01-20
Updated: 2019-01-20
Packaged: 2019-10-13 04:59:45
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,080
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17481647
Author URL: https://archiveofourown.org/users/SereneCalamity/pseuds/SereneCalamity
Summary: Clary had been waiting for them to figure out it wasn't anger that was burning between them.





	Crashing Together

**Author's Note:**

> I love these three together, if that's not already obvious. So here we go again! This one is dedicated to the lovely Reppinda5o3, who wanted the dynamic with Jace on top ;)  
> Disclaimer: I unfortunately own none of them.

They were fighting again.

Clarissa Morgenstern looked up from her coffee cup and over at them, rolling her eyes.

They fought  _a lot_.

Jace Herondale said Sebastian Verlac was a rude slob.

Sebastian said Jace was an arrogant prick.

They  _said_  it was a clash of personalities.

Clary knew for a  _fact_  it was just a whole lot of unresolved sexual tension.

They really just needed to fuck.

But they had to figure that out on their own, she'd already tried to and they hadn't listened.

She had a feeling that it was going to be coming soon, though.

So she was just going to sit back and watch it all unfold in front of her.

Today, they were fighting about who had left milk out on the bench while they had all been at class.

It had been Clary.

 _She_  wasn't about to say that, though.

Yesterday, they had been fighting because Sebastian left his shoes sprawled in the lounge.

The day before that, they had kissed for the first time.

Clary knew for a  _fact_  that was what was triggering their bitchiness toward each other even more so.

Jace had a thing about the flatmates all being tidy, but it verged onto OCD sometimes.

He got pissed at Clary sometimes, but they were fucking, so he managed to keep his annoyance under control.

Sebastian really just didn't give a shit, he was tidy, but he wasn't overly so.

Clary sipped from her coffee cup, shifting around where she was sitting on the bench.

The shouting was getting louder, and the topic of their argument shifted, for the third time.

 _Now_  they were talking about how Sebastian didn't do the washing last night, even though he said he would.

Clary rolled her eyes again, sipping from her coffee cup.

It was chipped and there was a printed picture of Winnie The Pooh on it.

Sebastian had brought it for her after their first 'date'.

And by date, they had gone bowling and then fucked in the employee's lounge, since Sebastian had a friend who worked there.

That had been two years ago.

Jace was crowding in on Sebastian now, and Sebastian was actually letting him.

Clary quirked an eyebrow.

 _That_  was new.

Usually the problem between the two of them was that they were both so stubborn.

Neither of them would back down.

They were both so dominant that they wouldn't admit they were wrong.

Not that Sebastian was admitting he was  _wrong_  or that he had left out the milk, but he was letting Jace advance.

It was because of the kiss.

It was  _definitely_  because of the kiss.

The three of them had been living together for a year and a half now.

Before then, she had just been with Jace, and she had been sleeping with him before she had met Sebastian.

Jace had been a little confused when she had introduced the pair of them to each other.

It wasn't as though her and Jace had been dating, they had both needed somewhere to live and that was how they ended up sharing an apartment. It wasn't long later they started sleeping together, but they had never put any boundaries in place, and for a while, Jace had still been sleeping with some other people.

Clary had been busy and she didn't wanted to sleep with anyone else, so she hadn't.

Until she met Sebastian.

And she had clicked with him.

So she propositioned both him and Sebastian, asking if they would go exclusive with her.

Surprisingly, they had both said yes.

Unsurprisingly, they clashed a lot.

Not over Clary, but over other shit.

When it came to Clary, they didn't  _argue_ , exactly.

They were just competitive.

It was fucking hot.

Okay, maybe it wasn't healthy, but Clary was a twenty-three year old female with two ridiculously attractive men in her bed.

She didn't really care.

Because when they were both fucking her, in one way or another, and they were staring at each other, all fire and sparks flying between them, it turned her on even more.

It wasn't like either of them were  _straight_.

She wasn't sure what was holding them back.

But after trying to press them together on more than one occasion, she had decided it was up to them.

There was a crash and then Clary's lips turned upwards.

It seemed that it was  _Sebastian_  who had gotten tired of waiting.

He had obviously backed down, let Jace crowd him into a wall, slumped his shoulders a little so that the inch of height between them was gone...And Jace still hadn't made a move.

The smile disappeared from Clary's lips as things progressed  _damn quick_.

She felt herself getting wet as Jace shoved Sebastian back onto the couch.

The three of them had had sex on that couch too many times to count.

But it was always  _them_  having sex with  _her_.

It was never them together.

It was Jace shoving himself into her mouth while Sebastian ate her out.

Or Sebastian fucking her ass while Jace was buried in her cunt.

Now, Jace was straddling Sebastian and they were tearing at each others clothes as though they were personally offending them. Clary could hear the literal ripping of material, and then they were both naked and they were kissing sloppily and loudly and she could hear them from where she was sitting.

Arousal flooded to the centre of her legs.

Sebastian made a move to grab Jace's shoulders but Jace just grabbed his wrist and shoved it backwards.

 _That_  was hot.

Both of them were dominant as hell in bed, something Clary was always happy to go with.

But watching Sebastian submit under Jace was so incredibly attractive.

He let out a long moan, thrusting his hips upward, and tugging a little at his hands, but not enough to pull away.

Clary slid off the couch, not wanting to interrupt what was happening, but wanting a closer look.

 _Shit_.

Jace bit at Sebastian's neck and Sebastians whine was high and needy.

Neither of the boys were paying her attention, which is what she wanted.

She just wanted them completely focused on each other.

Jace sucked his way down to Sebastian's collarbone, and there was definitely going to be a hickey there tomorrow.

There were going to be reddish-purple bruises marking him.

 _Jace's_  mark on him.

As they rolled their hips together, Clary caught glimpses of their cocks between them.

They were both so hard, and she could see the shine of pre-come on their abdomens.

Sebastian was lifting his head awkwardly off the pillow, chasing after Jace's lips as he pulled back.

Clary pressed her thighs together and leaned against the wall beside the couch.

Jace was  _purposefully_  pulling back.

He did it to Clary.

Made her chase after what she wanted, even if her arms were pinned above her head and she had limited range of movement.

Clary loved it, and from the whines and sighs coming from Sebastian, so did he.

After a few minutes of teasing, Jace kissed Sebastian again.

Hard and claiming.

He took one hand away from Sebastian's wrist, reaching between them, and there was a wrung out groan from Sebastian.

His hand kept pulling, and Sebastian's whole body was tight, jerking with the movement.

Jace glanced around, first to the table and then up to Clary, as though finally realizing she was there.

He looked back at the table and Clary knew what he was after.

 _Lube_.

She quickly walked over, her legs undoubtedly steadier than either of theirs, and opened up one of the drawers.

Jace pulled off Sebastian's cock and flattened his hand at her.

She squirted some of the cool liquid on and Jace moved further down Sebastian's legs, releasing the mans other wrist.

When he ordered Clary to sit on his face, and Sebastian to grip her thighs, there were groans from both of them.

She didn't even bother undressing properly, just jerked off her shorts and underwear, and then climbed on.

Sebastian's lips felt swollen and warm, undoubtedly from Jace's attention.

She could feel the moment Jace pressed a finger inside Sebastian, from Sebastian's reaction.

She  _wished_  she could see it.

His movements went slack for a few beats before he redoubled them, gripping her thighs so tight she was going to have marks.

Sebastian tongue was always talented, but having him eat her while groaning and writhing from Jace's attentions was something completely different.

 _Entirely_  different.

She came fast and violently the first time.

And then a second time not long after.

She felt shifting behind her and she forced herself to look over her shoulder.

Jace was moving between Sebastian's legs, and she could see three fingers were slick with lube.

He met her eyes, and there was this gleam in his eye that wasn't usually there.

She could place it, but she knew it was because of Sebastian.

And the look was something she  _liked_.

It wasn't competitive or angry, like it could sometimes get between them.

It was something else.

Clary moved off Sebastian's face, arranging herself on the ground beside him, on her knees.

Sebastian's lower face was covered in her juices and she couldn't help but lean forward to lick at his lips and chin.

He groaned, and then it changed to something much more guttural and Clary pulled back to look down.

Jace had pushed Sebastian's thighs back and up, folding him almost in half.

He was positioning himself _right there_ , and Clary could  _feel_  Sebastian's frustration with want for more.

Hell,  _she_  wanted this.

But Jace waited, waited until Sebastian looked at him properly, lifting his head and staring down, under Clary's face, where she was braced over him, through his parted thighs.

Jace arched an eyebrow, in a question.

Sebastian jerked his head in a nod, and then Jace was pushing forward.

Sebastian's whole body tensed up at the intrusion, even as he let out several deep breaths, trying to calm himself.

He had been with guys before, Clary knew that, but it would have been a while.

When Jace was fully seated inside him, he stroked a hand up Sebastian's thigh.

Sebastian let out another whine, and Clary stroked her fingers through his short hair, soothing him.

Then Jace was leaning forward.

He laid between Sebastian's thighs, bracing one hand next to his head, and then leaned forward to press a soft kiss to his mouth. Clary watched this exchange with wide eyes, as he gently licked at Sebastian's slack mouth and then pressed his tongue inside. Sebastian had one hand gripping Clary's shoulder and the other reached up to press against to Jace's chest, fingers spreading toward his collarbone.

Jace started to move, thrusting into Sebastian over and over again.

Clary couldn't decide where to look.

At where they were connecting so intimately further down the couch.

Or to where they were practically fucking each others mouths with their tongues.

She could feel even more stickiness between her thighs, insanely turned on by what was happening.

Jace pulled back from Sebastian to reach over and kiss Clary.

As he breathed against her mouth, laboured and hot, he told her to help Sebastian out.

She reached between their bodies, wrapping a hand around Sebastian and stroking him in time to Jace's thrusts.

Sebastian's whine was something that Clary could get herself off to for  _months_.

Jace's thrusts got harder and so Clary's quickened her pace.

Sebastian's fingers curled into her shoulder as he let out a loud moan, coating her fingers and his lower stomach in his come.

Jace wasn't far behind.

Afterwards, they all slumped onto the couch, Sebastian in the middle.

They were all messy, but none of them cared.

Clary was the first to giggle.

Sebastian let out a snort next.

Jace gave them a incredulous look, but Clary just rolled her eyes at him and then looked pointedly down at his half soft cock and the mess covering both men.

He let out a soft chuckle and then dropped a kiss to Sebastian's shoulder.

It was a tender moment.

Clary didn't say anything, because she didn't want to ruin it.

Talking was for later.

She curled up against Sebastian and reached out with a hand to touch her fingers on Jace's arm.

She was lulled to sleep by the sound of their breathing not long after.

**Let me know what you think x**

**Author's Note:**

> Let me know what you think x


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